Seismic design, modelling and assessment of self-centering steel frames using post-tensioned connections with web hourglass shape pins

A new self-centering steel post-tensioned connection using web hourglass shape pins (WHPs) has been recently developed and experimentally validated. The connection isolates inelastic deformations in WHPs, avoids damage in other connection parts as well as in beams and columns, and eliminates residual drifts. WHPs do not interfere with the composite slab and can be very easily replaced without bolting or welding, and so, the connection enables non-disruptive repair and rapid return to building occupancy in the aftermath of a strong earthquake. This paper presents a simplified nonlinear model for the connection and the associated beams and columns that consists of nonlinear beam-column elements, and hysteretic and contact zero-length spring elements appropriately placed in the beam-column interface. The model was calibrated against experimental results and found to accurately simulate the connection behaviour. A prototype building was selected and designed as a conventional steel moment-resisting frame (MRF) according to Eurocode 8 or as a self-centering steel MRF (SC-MRF) using the connection with WHPs. Seismic analyses results show that the conventional MRF and the SC-MRF have comparable peak storey drifts, and highlight the inherent potential of the SC-MRF to eliminate damage in beams and residual drifts. The paper also shows that repair of damage in the conventional MRF will be costly and disruptive after the design basis earthquake, and, not financially viable after the maximum considered earthquake due to large residual drifts.     

A comparison between rubble-pile and monolithic targets in impact simulations: Application to asteroid satellites and family size distributions

Collisions are a fundamental process in the creation of asteroid families and in satellite formation. For this reason, understanding the outcome of impacts is fundamental to the accurate modeling of the formation and evolution of such systems. Smoothed-Particle Hydrodynamics/N-body codes have become the techniques of choice to study large-scale impact outcomes, including both the fragmentation of the parent body and the gravitational interactions between fragments. It is now possible to apply this technique to targets with either monolithic or rubble-pile internal structures. In this paper we apply these numerical techniques to rubble-pile targets, extending previous investigations by Durda et al. (Durda, D.D., Bottke, W.F., Enke, B.L., Merline, W.J., Asphaug, E., Richardson, D.C., Leinhardt, Z.M. [2004]. Icarus 170, 243–257; Durda, D.D., Bottke, W.F., Nesvorný, D., Enke, B.L., Merline, W.J., Asphaug, E., Richardson, D.C. [2007]. Icarus 186, 498–516). The goals are to study asteroid–satellite formation and the morphology of the size–frequency distributions (SFDs) from 175 impact simulations covering a range of collision speeds, impact angles, and impactor sizes. Our results show that low-energy impacts into rubble-pile and monolithic targets produce different features in the resulting SFDs and that these are potentially diagnostic of the initial conditions for the impact and the internal structure of the parent bodies of asteroid families. In contrast, super-catastrophic events (i.e., high-energy impacts with large specific impact energy) result in SFDs that are similar to each other. We also find that rubble-pile targets are less efficient in producing satellites than their monolithic counterparts. However, some features, such as the secondary-to-primary diameter ratio and the relative separation of components in binary systems, are similar for these two different internal structures of parent bodies.     

Detecting crater ejecta‐blanket boundaries and constraining source crater regions for boulder tracks and elongated secondary craters on Eros

Abstract– We present results of a numerical model of the dynamics of ejecta emplacement on asteroid 433 Eros. Ejecta blocks represent the coarsest fraction of Eros’ regolith and are important, readily visible, “tracer particles” for crater ejecta‐blanket units that may be linked back to specific source craters. Model results show that the combination of irregular shape and rapid rotation of an asteroid can result in markedly asymmetric ejecta blankets (and, it follows, ejecta block spatial distribution), with locally very sharp/distinct boundaries. We mapped boulder number densities in NEAR‐Shoemaker MSI images across a portion of a predicted sharp ejecta‐blanket boundary associated with the crater Valentine and confirm a distinct and real ejecta‐blanket boundary, significant at least at the 3‐sigma level. Using our dynamical model, we “back track” the landing trajectories of three ejecta blocks with associated landing tracks in an effort to constrain potential source regions where those blocks were ejected from Eros’ surface in impact events. The observed skip distances of the blocks upon landing on Eros’ surface and the landing speeds and elevation angles derived from our model allow us to estimate the coefficient of restitution, ε, of Eros’ surface for impacts of 10‐m‐scale blocks at approximately 5 m s^?1 impact speeds. We find mean values of ε of approximately 0.09–0.18.     

The need for and use of socio-economic scenarios for climate change analysis: A new approach based on shared socio-economic pathways

Socio-economic scenarios constitute an important tool for exploring the long-term consequences of anthropogenic climate change and available response options. A more consistent use of socio-economic scenarios that would allow an integrated perspective on mitigation, adaptation and residual climate impacts remains a major challenge. We assert that the identification of a set of global narratives and socio-economic pathways offering scalability to different regional contexts, a reasonable coverage of key socio-economic dimensions and relevant futures, and a sophisticated approach to separating climate policy from counter-factual “no policy” scenarios would be an important step toward meeting this challenge. To this end, we introduce the concept of “shared socio-economic (reference) pathways”. Sufficient coverage of the relevant socio-economic dimensions may be achieved by locating the pathways along the dimensions of challenges to mitigation and to adaptation. The pathways should be specified in an iterative manner and with close collaboration between integrated assessment modelers and impact, adaptation and vulnerability researchers to assure coverage of key dimensions, sufficient scalability and widespread adoption. They can be used not only as inputs to analyses, but also to collect the results of different climate change analyses in a matrix defined by two dimensions: climate exposure as characterized by a radiative forcing or temperature level and socio-economic development as classified by the pathways. For some applications, socio-economic pathways may have to be augmented by “shared climate policy assumptions” capturing global components of climate policies that some studies may require as inputs. We conclude that the development of shared socio-economic (reference) pathways, and integrated socio-economic scenarios more broadly, is a useful focal point for collaborative efforts between integrated assessment and impact, adaptation and vulnerability researchers.     

Towards good governance of urban greening: insights from four initiatives in Melbourne,Australia

ABSTRACT

Urban greening can enhance sustainability and liveability, through conserving biodiversity, mitigating urban heat and enhancing people’s health and wellbeing. However, urban greening is complex, as it occurs in unique ecological settings, with social, cultural and economic factors shaping the forms it takes. This raises questions about the governance of urban greening, including what counts as ‘good governance’. In this paper, we first outline principles of good governance drawn from the natural resource management context. We then present four urban greening initiatives from Melbourne Australia representing different scales, land tenures and organising structures. Following this, we analyse how governance of the four initiatives addresses good governance principles. Our analysis shows that there are diverse ways in which urban greening can be practiced and governed. The importance of more ‘informal’ initiatives should not be discounted relative to formalised initiatives, as a spectrum of approaches can be seen as strength. Further, in determining what constitutes good governance, the standards against which initiatives are assessed should be tailored to their specific circumstances, and consider impacts to the environment itself. These findings point to good urban greening governance being both situated and principled.     

Calcite U–Pb age of the Cretaceous vertebrate‐bearing Bayn Shire Formation in the Eastern Gobi Desert of Mongolia: Usefulness of caliche for age determination

To verify the usefulness of calcite U–Pb measurement for vertebrate‐bearing strata in the Eastern Gobi, Mongolia, we performed laser ablation‐inductively coupled plasma‐mass spectrometry calcite U–Pb and trace element analyses of three caliche (calcrete) of the Bayn Shire Formation. The trace element analysis demonstrates high concentration of U in the calcites. Two meaningful calcite U–Pb ages were obtained; 95.9 ± 6.0 and 89.6 ± 4.0 Ma, which are consistent with published ages from the Bayn Shire Formation. Our results demonstrate that the calcite U–Pb method can be powerful tool for age determination of vertebrate‐bearing strata in the Gobi that do not contain index fossils or beds, but do contain caliches. This would make it possible for a comparison of biostratigraphy between the Gobi and other areas yielding abundant vertebrate fossils in Asia, North America and Europe, based on chronological data.     

Controls on at‐a‐station hydraulic geometry in steep headwater streams,Colorado, USA

Detailed hydraulic measurements were made in nine step‐pool, five cascade and one plane‐bed reach in Fraser Experimental Forest, Colorado to better understand at‐a‐station hydraulic geometry (AHG) relations in these channel types. Average values for AHG exponents, m (0·49), f (0·39), and b (0·16), were well within the range found by other researchers working in steep gradient channels. A principal component analysis (PCA) was used to compare the combined variations in all three exponents against five potential control variables: wood, D₈₄, grain‐size distribution (σ), coefficient of variation of pool volume, average roughness‐area (projected wetted area) and bed gradient. The gradient and average roughness‐area were found to be significantly related to the PCA axis scores, indicating that both driving and resisting forces influence the rates of change of velocity, depth and width with discharge. Further analysis of the exponents showed that reaches with m > b + f are most likely dominated by grain resistance and reaches below this value (m < b + f) are dominated by form resistance. Copyright © 2010 John Wiley & Sons, Ltd.     

Synoptic measurements of episodic offshore flow events in the central mid-Atlantic Bight

Sub-inertial across-shelf flows over the central mid-Atlantic Bight were examined using long-range CODAR SeaSonde type HF-radar surface velocities for the period August 2002 through February 2004. Across-shelf flow in this region was found to be episodic, with offshore flow occurring six times more often than onshore flow. Several recurring spatial patterns in offshore flow are identified, and two of these patterns emerge as statistically significant using empirical orthogonal functions. The most common type of offshore flow was a shelf-wide flow with events occurring throughout the year. The most energetic and well-defined shelf-wide flow events occurred during October through April, when the water column was less stratified. Other offshore flow patterns were more localized, with a flow at the bend or ‘point’ in the New Jersey coast being most common and most energetic. The offshore flow events identified here are capable of driving significant offshore transport, with more than one-third of offshore flow episodes having potential transport distances of greater than 14 km. In addition, clusters of multiple offshore flow events are shown to be capable of transporting near-surface material across much of the continental shelf.